Platelet monoamine oxidase activity in the psychoses: relationship to symptoms and lithium response.

The kinetics of platelet monoamine oxidase (MAO) were studied in 100 psychotic and manic patients and 36 controls. No relationship was found between MAO activity and response to lithium in the schizophrenic-like illnesses. However, the data do suggest there is an association between enzyme affinity (Km) and specific symptom clusters. Patients with the low Km variant of platelet MAO are enriched in depressive symptoms, while those with the high Km variant are enriched in manic symptoms.